A study of the mixture formation process of a diesel spray under phase change

Abstract

The purpose of this study was to analyze the structure and to clarify the mixture formation process within evaporative diesel spray. Liquid fuel was injected from a single-hole nozzle (l/d=1.0mm/0.2mm) into a constant-volume vessel under high pressure and temperature in order to visualize the spray phenomena. An exciplex fluorescence method was applied to the evaporative fuel spray to measure and investigate both the liquid and the vapor phase of the injected spray. The region of interest in this experiment was downstream towards the end of the spray. For accurate investigation, images of the liquid and vapor phase regions were recorded with a 35mm still camera and CCD camera, respectively. For the case of the evaporative fuel spray, the images showed that within the region of liquid phase very small droplets could be found outside of the spray and larger droplets at the spray’s tip. This can be explained through the droplet classification defined byStokes number (stk) (Chung et al., 1990). From the 2-dimensional analysis results of the heterogeneous distribution of the inner spray, a 3-dimensional analysis was attempted by using the offset incidence of the laser beam from the spray’s center axis. Finally, in order to quantify the mixture’s state change within the vapor phase region of the injected spray, images analysis were carried out based on the entropy of statistical thermodynamics.